Phenological Overlap Research Articles

THE GEOGRAPHICAL PATTERN OF SPECIATION AND FLORAL DIVERSIFICATION IN THE NEOTROPICS: THE TRIBE SINNINGIEAE (GESNERIACEAE) AS A CASE STUDY

The geographical pattern of speciation and the relationship between floral variation and species ranges were investigated in the tribe Sinningieae (Gesneriaceae), which is found mainly in the Atlantic forests of Brazil. Geographical distribution data recorded on a grid system of 0.5 x 0.5 degree intervals and a near-complete species-level phylogenetic tree of Sinningieae inferred from a simultaneous analysis of seven DNA regions were used to address the role of geographical isolation in speciation. Geographical range overlaps between sister lineages were measured across all nodes in the phylogenetic tree and analyzed in relation to relative ages estimated from branch lengths. Although there are several cases of species sympatry in Sinningieae, patterns of sympatry between sister taxa support the predominance of allopatric speciation. The pattern of sympatry between sister taxa is consistent with range shifts following allopatric speciation, except in one clade, in which the overlapping distribution of recent sister species indicates speciation within a restricted geographical area and involving changes in pollinators and habitats. The relationship between floral divergence and regional sympatry was also examined by analyzing floral contrasts, phenological overlap, and the degree of sympatry between sister clades. Morphological contrast between flowers is not increased in sympatry and phenological divergence is more apparent between allopatric clades than between sympatric clades. Therefore, our results failed to indicate a tendency for sympatric taxa to minimize morphological and phenological overlap (geographic exclusion and/or character displacement hypotheses). Instead, they point toward adaptation in phenology to local conditions and buildup of sympatries at random with respect to flower morphology. Additional studies at a lower geographical scale are needed to identify truely coexisting species and the components of their reproductive isolation.

Natural History of Mass-action in Predator-prey Models: A Case Study from Wolf Spiders and Grasshoppers

Abstract Mass-action models of predator-prey interactions assume that predators encounter prey according to their relative densities as scaled by functional responses, although models seldom specify critical natural history and behavioral mechanisms that ensure that encounters actually occur. As a case study of this assumption, we assess the hypothesis that daily and seasonal activity and microhabitat use by wandering wolf spiders (Lycosidae: Schizocosa) searching for four common grasshopper species (Orthoptera: Acrididae) are coincident under natural conditions. There was great overlap in seasonal phenology and use of microhabitats between spiders and grasshoppers. Grasshoppers that were suitably sized (10–20 mm in length) as prey for spiders were relatively abundant from late spring through summer in this grassland. Three of the four common grasshopper species used microhabitat in a similar way, but differed from a fourth common species, Phoetaliotes nebrascensis. However, when they were active, spiders...

Flowering phenologies of hummingbird plants from the temperate forest of southern South America: is there evidence of competitive displacement?

Plant species sharing pollinators may compete through pollination. This type of competition may lead to overdispersed flowering phenologies. However, phenological segregation is difficult to detect in seasonal climates. We compared patterns of phenological overlap in assemblages of ornithophilous plants from three localities of the temperate forest of southern South America with those generated by four different null models. These species were all visited and presumably pollinated by a single species, the hummingbird Sephanoides sephaniodes, which makes this situation ideal to evaluate the role of pollination‐mediated competition. For one site, we compiled data on flowering phenologies for three different years. Three models considered the flowering period of the whole assemblage of ornithophilous plants as the phenological window within which flowering phenologies were randomized, but made no further assumptions on how species should be distributed within that temporal frame. The fourth model assigned differential probabilities to different time intervals based on the flowering onset of non‐ornithophilous plant species. Observed mean pairwise overlaps for all localities and years were well within the interval defined by the 2.5 and 97.5% percentiles of the randomized distribution of expected mean pairwise overlaps according to models 1–3. However, model 4 showed a consistent trend towards overdispersion of ornihophilous phenologies, which show a shift towards mid‐ to late‐summer flowering. Thus, to the extent that the distribution of flowering of non‐ornithophilous species reflects the constraints imposed by a highly seasonal climate, our results provide support to the proposal that pollinator sharing may cause evolutionary displacement or ecological sorting of flowering phenologies. Other factors, such as phylogenetic inertia, could also contribute to explain extant phenological patterns in the highly endemic ornithophilous flora of the temperate forest of southern South America.

Variation in Reproductive Phenology in a Pinus radiata D. Don Seed Orchard in Northern Spain

Summary Reproductive phenology was studied in a Pinus radiata seed orchard, located in northern Spain. Timing of flowering was determined on the basis of data recorded by visual observations made in 2000, 2001 and 2002. The genetic and environmental factors affecting female and male phenology, as well as reproductive synchronization, were studied. The dates of beginning of the receptive phase and pollen shedding varied greatly from year to year but the variation on the sum of degree-days was low. In general, the flowering periods of the different clones overlapped. The clonal differences in the phenology of receptivity and pollen shedding were in most cases statistically significant. The time needed to reach flowering stages was under strong genetic control. Genetic control was stronger for the female than the male flowering process. However, correlations between years were stronger for male than for female flowering phenology. The male flowering clones that best synchronized with the females appeared to be those that started flowering earlier. The phenological overlap index varied greatly among clones, whether male or female, and also among years.

EVALUATION OF ECOLOGICAL RISK TO POPULATIONS OF A THREATENED PLANT FROM AN INVASIVE BIOCONTROL INSECT

Controversy exists over estimation of ecological risk in biological control. At present, the risk to the rare, federally listed Pitcher's thistle (Cirsium pitcheri )i nNorth America from Rhinocyllus conicus ,a biological control weevil now feeding on many native thistles, is unknown. We hypothesized that quantification of host specificity and potential phenological overlap between insect and plant would improve assessment of the magnitude of risk. In laboratory host specificity tests, we found no significant difference in R. conicus feeding or oviposition preference between the rare C. pitcheri and the targeted exotic weed (Carduus nutans )o rbetween C. pitcheri and Platte thistle (C. canescens), a closely related native North American species known to be affected by R. conicus .I na garden environment, R. conicus spontaneously found, oviposited, and developed completely on C. pitcheri .T aller plants with more flower heads were significantly more vulnerable, suggesting that the greatest impact is likely to be on individuals that generally contribute the most to recruitment and population persistence. For eight sites in two national parks over three years, the calculated period of expected R. conicus activity overlapped 99% and 78% of the flower heads initiated by C. pitcheri in the southern and the northern park, respectively. A de- mographic model suggests that population growth rate ( )o fC. pitcheri will decrease from 0.9897 to 0.8686, while time to halve the population will decrease from 66.9 to 4.9 years, under the conservative assumption that oviposition by R. conicus on C. pitcheri will occur at the same rate as on the related C. canescens. Calculated decreases in and t0.5 are larger if the rate of oviposition actually observed in the laboratory tests is used. These results indicate that the weevil poses a serious quantitative, demographic risk to the threatened C. pitcheri. The study supports the suggestion that ecological data can be used to improve the quantification of risk to native nontarget plant populations within the potential physiological host range of a biological control insect.

The potential for gene flow between cultivated and wild sunflower (Helianthus annuus) in the United States

The transfer of genes from crop plants to their wild relatives via hybridization has emerged as one of the primary risks associated with the commercialization of genetically engineered crops. Although previous studies have revealed relatively high levels of hybridization when crop plants come into contact with their wild relatives, the frequency of such contact across the range of cultivation of any crop taxon is unknown. Here we report the results of a multi-year, range-wide survey of the potential for reproductive contact between cultivated and common sunflower (Helianthus annuus). The results of this work indicate that the opportunity for crop-wild hybridization exists throughout the range of sunflower cultivation. Approximately two-thirds of all cultivated fields occurred in close proximity to, and flowered coincidentally with, common sunflower populations. In these populations, the phenological overlap was extensive, with 52-96% of all wilds flowering coincidentally with the adjacent cultivar field. Moreover, there was morphological evidence of hybridization in 10-33% of the populations surveyed within a given year. These findings indicate that crop-wild hybridization is likely across the range of sunflower cultivation in the USA.

A Phytosociological Study of Exotic Annual Brome Grasses in a Mixed Grass Prairie/Ponderosa Pine Forest Ecotone

The annual brome grasses, Bromus japonicus and B. tectorum, are common invaders of the Northern Great Plains. Our objective was to determine if these exotic plants were positively or negatively associated with particular plant species or functional types in a prairie/pine ecotone at Wind Cave National Park, South Dakota. We addressed this issue by sampling at two spatial scales—the landscape scale and the site scale. For the landscape we evaluated species associations across a 3800 ha ecotone using 90 transects. Annual bromes were positively associated with C3 grasses, particularly Agropyron smithii and Stipa viridula, in addition to the shrub Symphoricarpos occidentalis. Annual bromes were negatively associated with trees, C4 grasses, particularly A. gerardii, Bouteloua curtipendula and Schizachyrium scoparium, as well as the shrub Rhus aromatica. For the site scale we assessed relationships at a finer resolution within two 1 ha stands of grassland vegetation. Annual bromes were negatively associated with Poa pratensis in both stands. Results indicate that the bromes often dominate in portions of the landscape with C3 grasses and Symphoricarpos occidentalis. Within individual sites, the bromes appear most limited by a competitive interaction with P. pratensis, resulting from phenological overlap.

FACTORS FACILITATING SYNERGISTIC PREDATION: THE CENTRAL ROLE OF SYNCHRONY

Determining the phenological and diel concurrence of potentially overlapping predator guilds in a given system provides a gauge of the potential prevalence and importance of synergistic prey suppression. The phenology of pea aphids (Acyrthosiphon pisum) and ground- and foliar-foraging predators was determined through a combination of pitfall and sweep-net sampling in alfalfa. These results revealed diverse guilds of ground- and foliar-foraging predators with a high degree of phenological overlap among individual species. One of the most common ground-foraging predators, Harpalus pennsylvanicus, was found to be significantly more active at night, but also to maintain moderate activity levels during the day. When tested individually in simple arenas with full access to aphids, the aphid-consumption rates of five common ground-foraging predators (H. aeneus, H. pennsylvanicus, Amara familiaris, A. octopunctatum, and Philonthus spp.) were not significantly different from that of Coccinella septempunctata, a fo...

Nesting Phenology and Competition for Nest Sites among Red-Headed and Red-Bellied Woodpeckers and European Starlings

Nesting Phenology and Competition for Nest Sites among Red-Headed and Red-Bellied Woodpeckers and European Starlings

REPRODUCTIVE BIOLOGY OF ERYTHRONIUM GRANDIFLORUM VARIETIES GRANDIFLORUM AND CANDIDUM (LILIACEAE)

This four‐year (1982–1986) study compared the pollination biology and cytology of a relatively rare taxon, Erythronium grandiflorum Pursh var. candidum (Piper) Abrams, with that of a geographically widespread sister taxon, E. grandiflorum var. grandiflorum, in the Pacific Northwest. Breeding studies were used to study the reproductive systems of the taxa, to test for interfertility between them, and to seek abnormalities in the breeding system of the rare taxon that might account for its relative rarity. Chromosomes were counted in both taxa and in hybrids from artificial crosses. Ranges of the two taxa were determined from field studies and herbarium specimens. Although the ranges of the taxa overlap in part, populations are usually allopatric. Phenological factors are probably minor in preventing cross‐pollination between the taxa. Both taxa are protogynous obligate outcrossers pollinated by bees. Seed production apparently is not pollinator‐limited. The two taxa are interfertile only when individuals from allopatric populations are artificially crossed, and thus should be considered two biological species. When the taxa overlap in floral phenology in sympatric populations, they exhibit reciprocal incompatibility. Such incompatibility between closely related perennial species is unusual. It may have arisen via natural selection in mixed populations. Alternatively, if populations of each taxon vary with regard to their incompatibility alleles, they may have acquired their fertility barriers by chance before populations of the two taxa came into contact with each other.

Seed fall and phenological overlap in a guild of ant-dispersed herbs.

The timing of seed fall was studied in a guild of seven ant-dispersed forest herbs in NE-Zealand, Denmark. It is demonstrated, that the seed fall curves of Carex pilulifera, Melica uniflora and Luzula multiflora are remarkably different, representing logistic, hyperbolic, and linear relationships, respectively. The influence of environmental factors, and the significance to dispersal and predation, is discussed. It is suggested, that the three types of curves represent different strategies of seed fall. Simple, and explanded models of seed fall rate indicate that the density of seeds available to ants was more than 20 times greater for C. pilulifera than for M. uniflora. The observed phenological overlap of dispersal periods in the guild conformed to random expectations. Thus, the competition hypothesis was rejected, as there were no indications of a shift in phenology resulting from interspecific competition for the dispersal vector.

Coexistence of Five Sympatric Piper (Piperaceae) Species in a Tropical Dry Forest

Five Costa Rican species of Piper (Piperaceae) co—occur in evergreen forest sites at Santa Rosa National Park, Costa Rica. The species were found to have distinctive spatial distribution patterns with two species (Piper marginatum and P. pseudofuligineum) occurring in early successional sites and the others, P. amalago, P. jacquemontianum, and P. tuberculatum, occurring in less disturbed sites in dry forest, evergreen forest, and riparian forest, respectively. These habitat differences are associated with differences in seed and seedling biology and seasonal changes in the foraging behavior of the chiropteran seed dispersers of these plants. Excluding the uncommon P. tuberculatum, overall pairwise spatial overlap, measured by Pianka's (1974) symmetrical index, averaged 0.61. Relatively low phenological overlap allows the species to share animal visitors. Average pairwise flowering overlap (0.13) was about one—half the value of pairwise fruiting overlap (0.22). Responses to different rainfall cues and/or different inflorescence growth rates produce temporally separated phenological cycles. However, results of computer simulations suggest that observed phenological overlap was neither significantly lower nor significantly higher than expected by chance, for most pairs of species. Insect visitation is necessary for high seed—set, and species differ in their attractiveness to pollinators. Pairwise insect overlap (0.59) was greater than expected by chance, however. The plants also utilize the same six species of frugivorous bats as seed dispersers, and pairwise bat overlap was extremely high (0.96). Because they are important fruit sources for three common bat species, Piper species are keystone mutualists in dry tropical forests.

On the analysis of phenological overlap.

We briefly review current methods for detecting nonrandom patterns in the temporal overlap of flowering and fruiting curves. We discuss the assumptions behind these methods and propose a new method of analysis using computer simulations to measure n-wise, rather than pairwise, temporal overlap. We quantify the extent to which observed n-wise overlap differs from minimum possible n-wise overlap and apply our method to several data sets to test the hypothesis that interspecific competition for animal visitors has produced flowering curves whose overlap is less than that expected by chance. Results of our analyses provide little support for this hypothesis but suggest alternate criteria by which the species may be selected.

Overlap, Regularity, and Flowering Phenologies

Previous articleNext article No AccessNotes and CommentsOverlap, Regularity, and Flowering PhenologiesBlaine J. ColeBlaine J. Cole Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 117, Number 6Jun., 1981 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/283784 Views: 7Total views on this site Citations: 31Citations are reported from Crossref Copyright 1981 The University of ChicagoPDF download Crossref reports the following articles citing this article:Susanne S. Renner Placing the Time of Leaf Emergence in an Evolutionary Context, The American Naturalist 189, no.22 (Dec 2016): ii–iv.https://doi.org/10.1086/690020Ingi Agnarsson, Nicholas J. 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Pollinator Specificity in Lantana camara and L. trifolia (Verbenaceae)

Pollinator Specificity in Lantana camara and L. trifolia (Verbenaceae)